Shaft mounted structures, such as sheaves, gears, couplings, and the like, normally have one of two basic types of hubs for securing the structure to the shaft. The hub may be either bored-to-size, or drilled to the approximate size of the shaft and secured with a key, or the hub may have a tapered bore for accepting an oppositely tapered bushing, resulting in a wedged fit of the bushing and hub. The tapered hubs may include threaded and unthreaded half-holes or recesses formed in the inner wall thereof which correspond to unthreaded and threaded half-holes, respectively, formed in the outer wall of the bushing for accepting securing means, such as set screws. This application is concerned with the latter type, that is, shaft mounted structures having hubs with tapered bores. For tapered hubs, one of two general types of tapered bushing is normally used to secure the particular structure to the shaft. The tapered bushing may be a flush-mounted type with set screws as a securing means, normally used in installations where available space is limited, or where two structures, such as a sheave and a gear sprocket, must be mounted adjacent one another, or it may be a flanged bushing, having an annular, radially extending flange surrounding the large end of the body of the bushing.
Both types of bushings are of the split, contractible type, and, as the securing bolts are tightened and the oppositely tapered surfaces are drawn together, the bushing contracts around and securely grips the shaft. While some characteristics are shared by the two tapered bushing types, they are not designed to be interchangeable. This is mainly due to the different methods used to secure the bushings to the shafts. The flush-mounted type has unthreaded half-holes around the outer surface which correspond to threaded half-holes around the inner surface of the hub. As the set screws inserted therein are tightened, pressure against a shoulder of the unthreaded bushing half-holes forces the tapered surfaces to wedge together and forces the bushing to contract around and grip the shaft. To remove such bushings, a threaded half-hole is provided in the bushing which corresponds to an unthreaded half-hole in the hub. As a set screw is inserted therein and tightened, the bushing is forced outwardly by the pressure of the set screw against a shoulder of the half-hole in the hub, thereby disengaging its grip on the shaft and permitting its removal. In the flanged bushings, threaded and unthreaded holes are provided in the flange. Headed bolts or screws are inserted through the unthreaded holes in the flange and threaded into corresponding threaded holes in the hub to force the tapered surfaces together and mount the bushing. For removal, the bolts are threaded through the threaded holes in the flange and against a solid portion of the hub to force the tapered surfaces apart.
Thus, it can easily be seen that the two tapered bushing types are not interchangeable. If, for example, a flush-mounted bushing is required to replace a flanged bushing because of a reduction in available space caused by, say, the addition of another structure to the shaft, the structure itself must be changed along with the bushing, since the hubs are designed to accept one or the other type of bushing only. Therefore, both types of bushings, as well as shaft-mounted structures which will accept one or the other type, must be stocked or otherwise made available to meet varying demands.